This application is related and claims priority under 35 U.S.C. xc2xa7 119 to Japanese Patent Application No. 2000-370476, the entirety of which is incorporated by reference.
1. Field of the Invention
The present invention relates to a device and a method for polarizing a piezoelectric material in high-temperature gas.
2. Description of the Related Art
Examples of such a polarizing device include a type that polarizes a piezoelectric material by causing the temperature of the piezoelectric material to become a temperature required for polarization (that is, a polarization temperature) inside a constant-temperature bath, and a type that polarizes a piezoelectric material by heating the piezoelectric material to a required polarization temperature using a hot plate.
In the first type, since a constant-temperature bath is used, the temperature of the piezoelectric material can be caused to precisely become the polarization temperature. However, the rate at which the temperature of the piezoelectric rises is slow, and, since the piezoelectric material is placed in the constant-temperature bath while the piezoelectric material is at ordinary temperature, it takes time for the temperature of the piezoelectric material to reach the polarization temperature. Therefore, it takes a long time to polarize the piezoelectric material.
In addition, since it takes a long time to polarize one piezoelectric material, in order to reduce the time of polarizing many piezoelectric materials, a constant-temperature bath of a size that allows many piezoelectric materials to be placed in it at the same time is required, thereby increasing the size of the entire polarizing device.
In the second type, since the piezoelectric material is heated using a high-temperature hot plate, the temperature of the piezoelectric material rises at a high rate, so that the time required for the temperature of the piezoelectric material to reach a temperature near the polarization temperature can be made short. However, unlike a constant-temperature bath, it takes time to control the setting of the temperature of the piezoelectric material at the polarization temperature with high precision by controlling the temperature of the hot plate. Therefore, as in the first type, the result is that it takes a long time to polarize the piezoelectric material.
It is an object of the present invention to make it possible to set the temperature of a piezoelectric material at a polarization temperature with high precision within a short period of time, and to make it possible to control a plurality of piezoelectric materials.
It is another object of the present invention to make it possible to set the temperatures of a plurality of piezoelectric materials at a polarization temperature with high precision within a short time without increasing the size of the entire polarizing device.
Other objects will become apparent from the description below.
According to a first aspect of the present invention, there is provided a polarizing device that polarizes a piezoelectric material in high-temperature gas. The polarizing device comprises a temperature raising portion that raises the temperature of the piezoelectric material to a temperature required to polarize the piezoelectric material, and a constant-temperature bath having an atmosphere of gas that is kept at the required temperature and incorporating a polarizing portion that polarizes the piezoelectric material whose temperature is kept at the required temperature.
According to the present invention, since the piezoelectric material has its temperature raised at the temperature raising portion to the temperature required for polarization, when the piezoelectric material is placed into the constant-temperature bath, its temperature is set near the set temperature of the inside of the constant-temperature bath. Therefore, compared to the case where a piezoelectric material at normal temperature is placed in the constant-temperature bath, the time required for the temperature of the piezoelectric material to reach a desired temperature is considerably reduced.
Thereafter, the temperature of the piezoelectric material is set with high precision at the desired high temperature by the constant temperature bath. With the temperature of the piezoelectric material set at this desired temperature with high precision, polarization can be performed with respect to the piezoelectric material at the polarizing portion inside the constant temperature bath. Therefore, the piezoelectric material can be polarized in a short time with high precision.
In this case, since the temperature of one piezoelectric material can be set at the polarization temperature thereof in a short period of time, it is no longer necessary to use a large constant temperature bath to polarize a plurality of piezoelectric materials. Therefore, it is possible to prevent the size of the polarizing device from increasing.
In a first form of the first aspect, the constant-temperature bath further includes an aging portion that performs an aging operation on the piezoelectric material that has been polarized by the polarizing portion. When the first form is realized, it is possible to perform an aging operation on the piezoelectric material as it is at the aging portion, so that, compared to the case where an aging operation is performed on the piezoelectric material from ordinary temperature, the time taken to perform the aging operation can be greatly reduced. Therefore, this structure is preferable.
When the structure of the first aspect or the structure of the first form is used, there may be realized a second form of the first aspect in which the temperature-raising portion heats both surfaces of the piezoelectric material. When the second form is realized, the time required for the temperature of the piezoelectric material to reach the desired temperature can be further reduced. Therefore, this structure is preferable.
When the structure of the second form of the first aspect is used, there may be realized a third form of the first aspect in which the temperature-raising portion includes radiating heating means that heats one of the surfaces of the piezoelectric material by radiation of heat. When the third form is realized, not only one of the surfaces but also the inside of the piezoelectric material can be heated quickly and uniformly to a high temperature, so that the time for the temperature of the piezoelectric material to reach the desired temperature can be further reduced. Therefore, this structure is preferable.
The radiating heating means may be one using near-infrared rays, far infrared rays, or hot air for raising temperature, or any of the other types of radiating heating means.
When the structure of the second form of the first aspect is used, there may be realized a fourth form of the first aspect in which the temperature-raising portion includes means for directly heating the other surface of the piezoelectric material. When the fourth form is realized, the time required for the temperature of the piezoelectric material to reach the desired temperature can be further reduced. Therefore, this structure is preferable.
Examples of the means for direct heating includes a hot plate and any of the other types of means for direct heating.
When the structure of any one of the first form to the fourth form of the first aspect is used, there may be realized a fifth form of the first aspect in which the polarizing device further includes a transport mechanism that transports the piezoelectric material from the temperature-raising portion to the constant-temperature bath, and a control portion that controls transportation of the transport mechanism. The control portion carries out a control operation to operate the transport mechanism, so that the piezoelectric material can be transported from the temperature raising portion to the constant temperature bath. As a result, operations on the piezoelectric material, such as a temperature increasing operation, a constant temperature setting operation at the constant temperature bath, a polarizing operation, and an aging operation can be precisely set or controlled from the outside. Therefore, this structure is preferable.
When the structure of the fifth form of the first aspect is used, there may be realized a sixth form of the first aspect in which the control portion controls time for raising the temperature of the piezoelectric material by the temperature-raising portion, time for setting the temperature of the piezoelectric material at a constant temperature inside the constant-temperature bath, time for polarizing the piezoelectric material by the polarizing portion, and time for performing a or the aging operation by a or the aging portion in order to control the transportation of the transport mechanism based on the time controlling operations. When the sixth form is realized, the operation times of the piezoelectric material, such as the temperature raising time at the temperature raising portion, the constant temperature setting time at a constant temperature, the polarization time, and the aging operation time, can be precisely set. Therefore, this structure is preferable.
When the structure of the sixth form is used, there may be realized a seventh form of the first aspect in which the control portion controls each time so as to be the same or substantially the same. While transporting the piezoelectric material to the temperature raising portion, to the constant temperature setting portion, to the polarizing portion, and to the aging portion by the transport mechanism, the piezoelectric material is subjected to the required operations at the same timing durations. Therefore, it is easier to control the series of polarization operations on the piezoelectric material or to fabricate a piezoelectric material that is uniformly polarized with high precision, so that production yield is increased. Consequently, this structure is preferable.
When the structure of any one of the fifth to seventh forms of the first aspect is used, there may be realized an eighth form of the first aspect in which the piezoelectric material is transported by the transport mechanism while the piezoelectric material is placed at a transport jig. When the eighth form is realized, the production yield with respect to piezoelectric materials is increased.
When the structure of the eighth form of the first aspect is used, there may be realized a ninth form of the first aspect in which the transport jig is in the form of a pallet including a piezoelectric material holdable recess and a through hole in a bottom wall that defines the recess, in which a means or the means for direct heating that is provided at the temperature-raising portion is a hot plate, and in which the hot plate includes a heat transmitting protrusion and a heat transmitting contact surface, the heat transmitting protrusion being insertable into the through hole of the pallet and being contactable through the through hole with a bottom surface of the piezoelectric material that is held in the recess, and the heat transmitting contact surface being contactable with a bottom surface of the pallet.
In such a case, the pallet is heated as a result of coming into contact with the contact surface of the hot plate, so that the piezoelectric material is not cooled at the temperature raising portion, thereby precisely raising the temperature of the piezoelectric material at the temperature raising portion. Therefore, this structure is preferable from the point of view of allowing polarization operations with high precision.
According to a second aspect of the present invention, there is provided a method of polarizing a piezoelectric material inside high-temperature gas. The method comprises the steps of raising the temperature of the piezoelectric material to a temperature required to polarize the piezoelectric material, and polarizing the piezoelectric material as a result of placing the piezoelectric material into an atmosphere of gas whose temperature is maintained at the required temperature. By virtue of this method, the piezoelectric material can be polarized in a short time with high precision.
The method of polarizing a piezoelectric material inside high-temperature gas may further comprise the step of performing an aging operation on the polarized piezoelectric material in the same atmosphere of gas. By virtue of this method, compared to the case where the piezoelectric material is subjected to an aging operation from ordinary temperature, the aging operation time can be greatly reduced.